Flexible unbonded pipes of the present type are for example described in the standard “Recommended Practice for Flexible Pipe”, ANSI/API 17 B, fourth Edition, July 2008, and the standard “Specification for Unbonded Flexible Pipe”, ANSI/API 17J, Third edition, July 2008. Such pipes usually comprise an inner liner also often called an inner sealing sheath or an inner sheath, which forms a barrier against the outflow of the fluid which is conveyed in the bore of the pipe, and one or more armoring layers. In general flexible pipes are expected to have a lifetime of 20 years in operation.
Examples of unbonded flexible pipes are e.g. disclosed in WO0161232A1, U.S. Pat. No. 6,123,114 and U.S. Pat. No. 6,085,799.
The term “unbonded” means in this text that at least two of the layers including the armoring layers and polymer layers are not bonded to each other. In practice the known pipe normally comprises at least two armoring layers located outside the innermost sealing sheath and optionally an armor structure located inside the innermost sealing sheath normally referred to as a carcass.
These armoring layers comprise or consist of multiple elongated armoring elements that are not bonded to each other directly or indirectly via other layers along the pipe. Thereby the pipe becomes bendable and sufficiently flexible to roll up for transportation.
For many applications a pipe of the above type will need to fulfill a number of requirements. First of all the pipe should have a high mechanical strength to withstand the enormous forces it will be subjected to during transportation, deployment and operation. The internal pressure (from inside of the pipe and outwards) and the external pressure (from outside of the pipe) are usually very high and may vary considerably along the length of the pipeline, particular when applied at varying water depths. If the internal pressure of the pipe exceeds the load bearing capacity of the armoring elements of the armoring layers located outside the innermost sealing sheath, the internal pressure will ultimately result in damage of the pipe e.g. by upheaval buckling and/or burst of the flexible pipe. Unbonded flexible pipes which are to be deployed at deep water and/or which are to be subjected to high internal pressures therefore often comprise a pressure armor which is a layer of helically wound armor elements, wound on the outer side of the innermost sealing sheath and with a relative steep angle to the longitudinal center axis of the pipe e.g. of about 70 degrees or higher. In order to ensure that the windings of the helically wound armor elements of the pressure armor are do not separate to much from each other during deployment and during use under high internal pressure, the windings of the helically wound armor elements of the pressure armor layer are usually interlocked to each other since an increased and uncontrolled gap between windings of the helically wound armor elements provides an increased risk of damage to the sealing sheath and burst of the flexible pipe.
Such unbonded flexible pipes with interlocked pressure armors are for example described in U.S. Pat. No. 6,065,501 and US 2011/0030831.
The interlocking of the helically wound armor elements of the pressure armor layer is, however, rather cumbersome and expensive and further results in limitation of possible types of armor elements that can be applied.